The TO-220 package is a known industry standard. The package includes a thermally conductive base which is preferably metal and on which a semiconductor device is mounted with low thermal impedance between the device and the base. The device may also be electrically connected to the base. The semiconductor device and a portion of the frame are typically encapsulated by a resin material, which protects the device from its environment. A locking projection typically extends from the base to the outside of the protective epoxy and is fastened to the external mounting surface to draw heat from the device. Also included are lead terminals which extend outside the resin body and include bonding pads to which a wire bond connection is provided from the device to the leads.
In a surface mount device, the surface of the base that is adjacent to the circuit board and opposite from the device is exposed for electrical contact to the circuit board.
Typically, the leads are bent outside the resin body to contact the surface and provide electrical connection to the circuit board. This bend in the leads, however, can cause mechanical stresses in the resin body.
Moreover, two gauges of metal are typically used. A thick gauge metal is used for the base, and a thin gauge metal is used for the leads so that they may be bent. This use of two gauges increases the complexity of the manufacture of the package device.